Changing the Title Line of a Thread Well After The Thread Has Matured.
If we were to agree to allow an OP to change the Title of a thread that ability would probably have to be universal throughout the Forums.
Whenever, I notice that a significant change has occurred within a Rental thread I routinely change the title without being asked; but sometimes watching the Forum for such needed change is not practical.
Although TUG allows a change to a Title of a Thread to exist for a short period of time to allow the OP the opportunity to edit the Title immediately after posting, that ability goes away once the Thread has matured and had the opportunity to have responses.
The ability to adjust the title after the short time frame has passed is then an administrative function that can only be done by an Administrator or Moderator.
As Denise has already advised, just PM any Moderator.
Meanwhile, keep in mind that there is probably a very good reason for the cut-off in editing.
Think of it this way, if any OP had that ability and exercised it periodically throughout the Forums the ability to easily find or follow a thread that has aged would be compromised.